How can I get the length of an array in awk?

This command

echo "hello world" | awk '{split($0, array, " ")} END{print length(array) }'

does not work for me and gives this error message

awk: line 1: illegal reference to array array

Why?

When you split an array, the number of elements is returned, so you can say:

echo "hello world" | awk '{n=split($0, array, " ")} END{print n }'
# ------------------------^^^--------------------------------^^

Output is:

2